Copolyester is the modified form of polyesters, which are combinations of diols and diacids. For instance, if we introduce diacids, like isophthalic acid, or diols, like cyclohexane dimethanol to the polyester polyethylene terephthalate (PET), the material turns into a copolyester. For example, by introducing other diacids, such as isophthalic acid (IPA), or other diols, such as cyclohexane dimethanol (CHDM) to the polyester polyethylene terephthalate (PET), the material becomes a copolyester due to its comonomer content.